A metamaterial is a composite material that derives a material property from a combination of its constituent element and its structure rather than exclusively from its bulk composition. In particular, metamaterials are manmade materials that generally comprise arrays (i.e., both periodic and aperiodic) of elements. The elements, which are usually much smaller than a wavelength of an excitation signal, act together to produce a collective response (or material response) to the excitation signal. For example, metamaterials that exhibit a negative index of refraction (so-called negative index materials (NIMs)), a material property that is not available in natural materials, have been demonstrated. Such metamaterials may be realized by a periodic structure that exhibits at certain frequencies both a negative permittivity ∈ and a negative permeability μ, for example. Metamaterials have a number of intriguing real-world applications including, but not limited to, producing a so-called superlens which may provide resolutions that exceed a standard diffraction limit at an operational wavelength, providing strong polarization rotation and even implementing “cloaking devices” that could make an object substantially invisible to incident electromagnetic radiation.
Metamaterials in both the microwave and optical domains have been demonstrated beginning with work by W. E. Kock in the 1940's. Kock developed metal lens antennas and metallic delay lines that, while not described at the time as such, essentially comprised metamaterials. Note that the term ‘metamaterial’ was first coined in 1999 by R. M. Walser and has been used only more recently to describe composite materials including, but not limited to, those developed by Kock and others prior to the 1990's.
Optical metamaterials have also been demonstrated. Optical metamaterials may be realized by constructing an array of elements with sub-wavelength dimensions that exhibit a response (i.e., resonance) to one or both of an electric field component and a magnetic field component of an optical excitation signal. N. Liu et al. and others have separately reported a number of examples of optical metamaterials comprising a periodic array of elements that exhibit relatively strong electric field responses. Such optical metamaterials that operate in the infrared and optical wavelengths are also known as photonic metamaterials.
Chiral metamaterials are a relatively new class of metamaterials that employ elements that are chiral. Chiral metamaterials often are more readily realizable, especially at optical frequencies. Bingham Wang et al., A. V. Rogacheva et al., Do-Hoon Kwon et al., and others have described various chiral photonic metamaterials comprising split-ring resonators and tetra-gammadions.
Certain embodiments of the present invention have other features that are one of in addition to and in lieu of the features illustrated in the above-referenced figures. These and other features of the invention are detailed below with reference to the preceding drawings.